Spacecraft, particularly those with or electro-optic/infrared (EO/IR) sensor systems, typically include various types of sensors for capturing images, computers for processing information, and communication modules for transmitting data to and receiving data from external systems. Thus, such spacecraft often include a pulse tube expander or Stirling cycle cryogenic cooler to remove heat from the sensors and/or to cool the sensors to very low temperatures (for example 65 Kelvin). Cryogenic coolers generally include several moving components, such as a compressor piston, a motorized driver for that compressor piston, a expander piston (also referred to as a displacer piston), a motorized driver for that displacer piston, balancer pistons, and motorized drivers for each of the balancer pistons. These moving components can generate vibrations.
Space-borne EO/IR systems frequently cannot tolerate vibration disturbances, and in some such applications may not warrant the cost and/or complexity of a cryoradiator. In particular, most (if not all) sensitive space EO/IR systems use control moment gyroscopes (CMGs, or “gyrodynes”) for inertial control of the vehicle. The CMGs spin at, for example, 100 Hertz (Hz), requiring all structures to be designed to not resonate at 100 Hz in order to avoid line-of-sight jitter. Any cryocooler operating within such a spacecraft may be permitted to have greater exported disturbances than if operating at any frequency other than 100 HZ, with higher frequencies also improving disturbance roll-off associated with vibration isolators and eliminating the need for launch locks. However, most existing pulse tube expander and Stirling cycle space cryocoolers suitable for IR focal plane array (FPA) cooling operate at frequencies between 30 and 70 Hz (often the worst frequencies for exported disturbance), causing vibration of sensitive optical systems.
There is, therefore, a need in the art for a low cost cryocooler designed to be compatible with existing CMG operating frequencies.